The conversation comes as the US has increased diplomatic pressure on China to convince North Korea to give up its nuclear weapons program and stop its provocative behavior toward South Korea. The US held joint military drills with the South last week, and US Secretary of State Hillary Clinton is due to meet with Japanese and South Korean officials today to discuss the situation.

In a phone call placed overnight US time, Obama “urged China to work with us and others to send a clear message to North Korea that its provocations are unacceptable,” according to the White House. He condemned North Korea’s attack on Yeonpyeong and its uranium enrichment program.

Chinese state-run news agency Xinhua reports that President Hu “called for a calm and rational response from all sides” to prevent the situation from escalating, and said he is “greatly concerned” about the crisis. "To relax tension, not aggravate it, to seek dialogue, not confrontation, and to pursue peace, not war, this is the strong aspiration and call of the peoples in both sides of the Korean Peninsula and of the international community," he said according to Xinhua.

South Korea’s live-firing drills, which began Monday, are similar to those that North Korea says prompted its attack, reports Bloomberg. The North yesterday warned of "catastrophic consequences” for the military exercises. The South Korean minister of defense, meanwhile, said Monday that the South would invoke the right to self defense in the case of another attack by the North, regardless of the rules of engagement that govern the US-led United Nations force in the South, reports The Korea Times.

The Washington Post reports that the US has increased pressure on China to rein in the North while redefining ties with South Korea and Japan, “potentially creating an anti-China bloc in Northeast Asia that officials say they don't want but may need.” The Post reports that tone of the US relationship with China is deteriorating ahead of a meeting between Obama and Hu in January, and quotes a senior administration official as saying “we think the Chinese have been enabling North Korea.”

The U.S. exasperation with China over the Koreas has been evident since June, when President Obama accused China of "willful blindness" in remaining silent over North Korea's suspected sinking of a South Korean warship in March. But the administration's position now that China is in effect partially to blame for the problems is new. […]While the new U.S. position reflects a growing frustration with China's apparent unwillingness to rein in Pyongyang, it also underscores a sense that the United States and South Korea have run out of leverage with the North and are therefore left dependent on Beijing for a solution to the security of the peninsula.